What neighbourhood factors support more transport walking as adults age? A five-wave longitudinal multilevel cohort study in Brisbane, Australia.

Introduction: Transport walking is a simple, cost-effective and sustainable way to promote physical activity that integrates movement into daily routines. A supportive built environment, including walkable areas-consisting of high residential density, good street connectivity and mixed land-uses-is associated with greater transport walking, making it a critical area for urban planning and policy interventions. However, most studies on age differences in built environment and transport walking are cross-sectional, limiting causal inference and emphasising the need for longitudinal research to strengthen evidence for healthy ageing policies. Methods: This study longitudinally examines age interaction effects with built environment attributes on transport walking, incorporating time-varying exposures and confounders, and accounting for neighbourhood self-selection. Data were from the How Areas in Brisbane Influence HealTh and AcTivity study, a five-wave multilevel cohort study from (2007-2016). Analysis used participants residing at the same address throughout the study. Transport walking was self-reported and classified as walkers or non-walkers. Generalised linear mixed-effects models were used to assess associations between the built environment and transport walking, and their interaction with age, adjusting for sociodemographic factors, length of residence, neighbourhood preference and neighbourhood disadvantage. Results: Higher residential density, street connectivity, land-use mix and walkability were longitudinally associated with greater transport walking. Interaction effects showed that older adults were more likely than younger adults to engage in transport walking in denser, more walkable neighbourhoods. Conclusion: More walkable neighbourhood environments, characterised by higher residential density, street connectivity and land-use mix, were associated with a greater likelihood of transport walking over time. Moreover, the associations with density and walkability were stronger at older ages, suggesting that these attributes may play an important role in supporting healthy ageing.